(Kopp, 1982). The ability to exercise self-control increases from 18 to 30 months and becomes more stable across time and across situations (Vaughn et al., 1984).

The capacity to use developing executive function to regulate behavior and emotions in the service of social goals and situational demands is sometimes referred to as inhibitory or effortful control, as discussed above. Because many skills, competencies, and experiences affect whether a child can regulate his or her emotions and behavior, researchers have used a wide variety of tasks to assess individual differences in effortful control. These tasks include being able to shift with ease from doing something as “fast as you can” to “as slow as you can” to being able to “not peek” when waiting for a surprise gift, to being able to play games like Simons Says. When individual differences on such tasks are assessed and averaged, they provide one window into why some children comply more readily with adult requests not to touch interesting things even when the parent is not watching and more readily resist the temptation to cheat on games even when they think they will not be caught. Being good at effortful control tasks, including those that more directly assess executive functioning, doesn't mean that a child will behave in compliance with social rules that require self-control, however. Aspects of children's relations with others that motivate them to want to adopt the rules of their group also matter (Kochanska, 1990).

A number of researchers have investigated the developmental trajectories of executive function by presenting children with a battery of tests purported to measure different aspects of this domain of regulatory behavior (e.g., Gnys and Willis, 1991; Levin et al., 1991; Welsh et al., 1991). The focus here is not on precursors of executive function, but on manifestations of behaviors that constitute components of this construct. These studies have demonstrated that the different component skills involved in executive functioning show different developmental trajectories and mature at different rates. In one of the first studies to include preschoolers, children ages 3 to 12 were presented with a series of tasks that involved visual searching, verbal fluency, motor planning, planning sequences, the ability to respond flexibly to changes in the environment, and the capacity to inhibit responses (Welsh et al., 1991). Patterns of performance on these measures indicated that three underlying factors captured children's responses: (1) fluid and speeded response (2) hypothesis testing and impulse control and (3) planning. The investigators interpreted their findings as evidence for stage-like development, with the first stage beginning around age 6, the next stage around age 10, and the final stage during adolescence. Six-year-olds, for example, were able to perform as well as adults on tasks that involved visual searching and planning simple sequences, whereas it was not until adolescence that the ability to plan complex sequences, verbal fluency, and motor planning reached maturity.



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